Phase transitions of a single polyelectrolyte in a poor solvent with explicit counterions

TL;DR

This study uses molecular dynamics simulations to explore phase transitions of a single polyelectrolyte in a poor solvent, revealing a first-order transition and counterion condensation effects.

Contribution

It provides new simulation-based evidence for phase transition types and clarifies the nature of intermediate phases in polyelectrolyte behavior.

Findings

First-order transition from extended to collapsed phase

Counterion condensation transition with critical exponents

Finite size effects influence the perceived intermediate phase

Abstract

Conformational properties of a single flexible polyelectrolyte chain in a poor solvent are studied using constant temperature molecular dynamics simulation. The effects of counterions are explicitly taken in to account. Structural properties of various phases and the transition between these phases are studied by tracking the values of asphericity, radius of gyration, fraction of condensed counterions, number of non-bonded neighbours and Coulomb interaction energies. From our simulations, we find strong evidence for a first-order phase transition from extended to collapsed phase consistent with earlier theoretical predictions. We also identify a continuous phase transition associated with the condensation of counterions and estimate the critical exponents associated with the transition. Finally, we argue that previous suggestions of existence of an independent intermediate phase between extended and collapsed phases is only a finite size effect.